Tubeless tires require compositions having high air retention. Bromobutyl and chlorobutyl rubbers are the polymers of choice for air-retention in tubeless tires. Similarly, brominated poly(isobutylene-co-p-methylstyrene) (BIMS), such as disclosed in U.S. Pat. Nos. 5,162,445 and 5,698,640, is typically used when heat resistance is of importance. The selection of ingredients for the commercial formulations of elastomers depends upon the balance of properties desired and the application end use. For example, in the tire industry, processing properties of the green (uncured) compound in the tire plant versus in-service performance of the cured rubber tire composite, and the nature of the tire, i.e. bias versus radial tire, and passenger versus truck versus aircraft tire, are all important considerations that must be balanced.
One method to alter product properties and improve air barrier properties is to add clay to an elastomer to form a “nanocomposite”. Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. A common type of inorganic particle used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays”. Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have near complete exfoliation, wherein the polymer is fully dispersed or intercalated with the individual nanometer-size clay platelets. Due to the general enhancement in air barrier qualities of various polymer compositions when clays are present, there is a desire to have a nanocomposite with low air permeability.
Nanocomposites have been formed using brominated copolymers of isobutylene and p-methylstyrene. See, for example, Elspass et. al., U.S. Pat. Nos. 5,807,629, 5,883,173, and 6,034,164. Further improvement in the uncured and cured properties of these elastomeric compositions can be achieved by the use of processing aids. For example, resins and oils (or other “processing aids”) such as naphthalenic, paraffinic, and aliphatic resins may be used to improve the processability of elastomeric compounds. However, increased processability often comes at the price of a loss of air impermeability and an increase in undesirable effects of various other properties. Yet another possible negative impact is the release of processing aids into the final product, and the effect degradation products have on the overall properties of the matrix.
In order to produce nanocomposites, organoclays must be exfoliated. Exfoliation of organoclays may be accomplished using an intercalant. At least partially intercalated organoclays may also be produced through solution based ion-exchange reactions that replace sodium ions that exist on the surface of particular clays, e.g., sodium montmorillonite, with alkyl or aryl ammonium compounds. One of the deficiencies of this method is the limited thermal stability of the amines. Another deficiency is the lack of chemical bonding between the clay and the polymer matrix the clay is distributed in. These deficiencies often lead to poor mechanical properties and reduced processing characteristics.
One method to improve the organoclay performance is to use functionalized polymers to treat the clay. This approach has been limited to materials that are soluble in water or to materials that can be incorporated into the polymerization reaction. This approach has been used to prepare nylon nanocomposites, using for example, oligomeric and monomeric caprolactam as the modifier. Polyolefin nanocomposites have utilized maleic anhydride grafted polyolefins to achieve some success in the formation of nanocomposites.
For example, it is known to utilize exfoliated-clay filled nylon as a high impact plastic matrix, such as disclosed in U.S. Pat. No. 6,060,549 to Li et al. In particular, Li et al. disclose a blend of a thermoplastic resin such as nylon and a copolymer of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene), the blend also including nylon containing exfoliated-clays that are used as a high impact material. Further, Japanese Unexamined Application P2000-160024 to Yuichi et al. discloses a thermoplastic elastomer composition which can be used as an air barrier. The nanocomposite in Yuichi et al. includes is blend similar to that disclosed in Li et al.
Nanocomposites have also been formed using brominated copolymers of isobutylene and para-methylstyrene. See, for example, Elspass et. al., U.S. Pat. No. 5,807,629, U.S. Pat. No. 5,883,173, and U.S. Pat. No. 6,034,164. It has been found that the efficiency of clay exfoliation is increased by increasing bromination level of the polymer. Unfortunately, these copolymers are very reactive and it is difficult to achieve high levels of functionalization without undue added vulcanization. Optimal performance in many applications requires the minimum level of vulcanization that yields acceptable physical properties, in that way aging and durability of the compositions are maximized.
Thus, there is still a problem of achieving a nanocomposite suitable for an air barrier, in particular, an air barrier incorporating the copolymer (or “interpolymer”) of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene). Enhancement of processability properties of such copolymers tends to result in copolymers having poor air barrier properties. What is needed is an exfoliated nanocomposite of a halogenated copolymer of a C4 to C7 isomonoolefin, a para-methylstyrene and a para-(halomethylstyrene), having both air barrier properties and improved processability properties.